1. Field of The Invention
The present invention relates generally to liquid crystal displays (LCDs) and, more particularly, to controlling the contrast with which data is displayed on an LCD device.
2. Related Art
Sudden cardiac arrest has been attributed to over 350,000 deaths each year in the United States, making it one of the country""s leading medical emergencies. Sudden cardiac arrest is a disruption of the natural heart""s functioning, causing a lack of blood flow to vital organs. In a majority of instances, sudden cardiac arrest is manifested as an abnormal or chaotic heart rhythm, called fibrillation. These instances are generally identifiable by the victim""s immediate loss of pulse, loss of consciousness and a cessation of breathing. Unless immediate medical intervention is initiated, sudden cardiac arrest can lead to death within a matter of minutes.
The critical components of medical treatment that must be administered to a victim of sudden cardiac arrest include (1) early access to emergency care; (2) early cardiopulmonary resuscitation to maintain blood oxygenation and flow to the victim""s brain and other vital organs; (3) early defibrillation to restore the heart""s regular rhythm; and (4) early access to advanced medical care. If cardiopulmonary arrest is followed by defibrillation within about four minutes, a victim""s chance of survival can approach or exceed fifty percent. Prompt administration of defibrillation within the first critical minutes is considered one of the most important components of emergency medical treatment for preventing death from sudden cardiac arrest.
To achieve this, portable defibrillators have been developed that can be carried to a victim""s location to defibrillate the victim prior to reaching a hospital. Initially, portable defibrillators were manually-controlled, sophisticated devices that could be used safely only by specially-trained medical personnel. More recently, however, defibrillators with advanced decision making functions, commonly known as automatic or semi-automatic external defibrillators (AEDs) have been developed. AEDs can be used safely by first responders with less advanced medical training.
There has been a trend to install these more advanced AEDs in public facilities such as shopping malls, hotels, commercial aircraft, stadiums, sports arenas, concert halls and the like, as well as to equip emergency response vehicles such as EMS vehicles, fire engines and police cars with such devices. These AEDs are subject to a wide range of environmental conditions. In particular, AEDs may be stored in a vehicle or facility for extended periods of time, subject to vibration, heat, etc. Beyond storage and transportation, these AEDs must also be capable of operating in a myriad of environmental conditions. For example, an AED may be required to operate in the dark, shade or direct sunlight; in precipitation as well as dry or humid conditions, etc.
Typical AEDs include a liquid crystal display (LCD) screen or panel, referred to generally herein as an LCD device. The LCD device may display a wide range of data to an operator during a resuscitation, including device status information, patient monitoring information, operator instructions and the like. The environmental conditions in which an AED must operate often effect adversely the ability of an operator to view clearly such information displayed on the LCD device. One environmental condition of particular relevance to the present application is ambient temperature.
Due to the above-noted storage, transportation and operating conditions, AEDs must be capable of performing reliably in a wide range of ambient temperatures that may be significantly greater than the temperature range that the LCD devices are designed to operate within, referred to herein as the normal or standard temperature range. For example, during a single use an AED may be transferred in a matter of minutes from a vehicle storage compartment wherein the ambient temperature exceeds 55xc2x0 C. to an indoor facility wherein the ambient temperature is less than 20xc2x0 C., at which immediate, reliable performance is required. In addition, use of the defibrillator in direct sunlight or in varying combinations of sunlight and shade may be required, all of which require data to be displayed with the appropriate contrast to enable the operator to view clearly the displayed data.
Unfortunately, many commonly available LCD devices exhibit poor or limited contrast characteristics when subject to high ambient temperatures, even those that are just slightly greater than the standard operating temperature. As a result, an operator of a defibrillator incorporating such an LCD device may be unable to visualize the displayed data when attempting to resuscitate a victim, or may have to relocate the victim to an environment in which the temperature is suitable for the LCD. Such delays only serve to decrease the likelihood of a successful resuscitation.
The present invention is directed to a liquid crystal display (LCD) device temperature compensation control system and associated methodologies. The invention controls the contrast voltage provided to the LCD device based on the ambient temperature of the LCD to enable the LCD to display data beyond the standard, manufacturer-specified operational temperature range or to improve the contrast when operating within the normal ambient temperature range.
Generally, the contrast ratio (luminance with all pixels white divided by luminance with all pixels black) of an LCD display depends primarily on ambient temperature. Generally, at a given ambient temperature an LCD device displays data with a range of contrast ratios in response to a range of corresponding contrast voltages provided to the LCD device. Beyond this standard contrast voltage/ambient temperature operational range the contrast ratio is approximately one; that is, all LCD device segments or regions (pixels) are either substantially white or substantially black. As noted, for certain implementing systems such as automatic and semi-automatic external defibrillators (AEDs), operating within this standard operating range may be insufficient to insure that the LCD device will display data with the requisite contrast in the anticipated operational environments.
The inventor has found that certain LCD devices can be controlled so that they contrast voltage/ambient temperature operational ranges. The first is the noted standard operating range. The second operational range in these LCD devices is separate and distinct from the standard operating range. The second operational range is effective for ambient temperatures that are greater than or equal to the high temperature region of the standard operating range. As such, this second operational range is referred to herein as the extended operating range. Thus, such an LCD device is controlled in accordance with two modes of operation: A standard operational mode and an extended operational mode. At normal ambient temperatures, the LCD device is controlled in accordance with the standard operational mode, the LCD device is controlled such that the relationship between the contrast voltage and ambient temperature is represented by the standard operating range. At ambient temperatures greater than or equal to those associated with the standard operating range, the LCD device is controlled in accordance with the extended operational mode. Here, application of a sufficient contrast voltage causes these certain LCD devices to improve the contrast of displayed data or to once again display previously non-visible data with a contrast ratio suitable to provide some visibility. Thus, the present invention takes advantage of the ability of the LCD device to operate in this second, extended operating range, controlling the contrast voltage supplied to the LCD device based on ambient temperature such that the LCD device operates within either the standard or extended operating range to achieve an optimum contrast ratio.
In connection with certain types of LCD devices, the present invention also adjusts the frame rate and/or data inversion state of the displayed data. With regard to frame rate, when subjected to higher ambient temperatures, the contrast of an LCD device improves with an increase in frame rate. Conversely, when subjected to lower ambient temperatures, the contrast of an LCD device degrades with an increase in frame rate. Aspects of the present invention select a frame rate based on the ambient temperature in which the device is being operated to further optimize the contrast of the displayed data. In one embodiment in which the above behavior is exhibited, the selected frame rate is controlled so as to correlate with changes in ambient temperature; that is, the frame rate is increased with an increase in ambient temperature, and is decreased with a decrease in ambient temperature.
With regard to data inversion state, LCDs commonly have two data inversion states: a normal display state in which black characters are presented on a white background, and an inverted display state in which white characters are displayed on a black background. The inventor has found that the liquid crystals in certain of the noted LCD devices behave unexpectedly when operating within the extended operating range. Specifically, the liquid crystals behave so as to invert the displayed data. To insure continuity of the display from the perspective of the operator, aspects of the present invention cause the inversion of the data provided to the LCD device under such conditions. This inverted data is then inverted again by the LCD device, resulting in a display of data having the same inversion state for the standard and extended operational modes.
A number of aspects of the invention are summarized below, along with different embodiments that may be implemented for each of the summarized aspects. It should be understood that the summarized embodiments are not necessarily inclusive or exclusive of each other and may be combined in any manner in connection with the same or different aspects that is non-conflicting and otherwise possible. These disclosed aspects of the invention, which are directed primarily to LCD contrast control systems and methodologies, are exemplary aspects only and are also to be considered non-limiting.
In one aspect of the invention, an apparatus for controlling a contrast voltage applied to an LCD device is disclosed. The contrast voltage is based on a current ambient temperature so as to cause data to be displayed on the LCD device with a contrast ratio that is associated with the applied contrast voltage and current ambient temperature. The applied contrast voltage is determined in accordance with a standard operating range and an extended operating range of ambient temperatures each of which having a corresponding range of contrast voltages. The applied contrast voltage is set in accordance with the standard operating range when the ambient temperature is below a first ambient temperature and is set in accordance with the extended operating range when the ambient temperature is greater than a second ambient temperature.
In accordance with another aspect of the present invention, an LCD device temperature compensation control system is disclosed. The system controls a contrast voltage provided to an LCD device based on ambient temperature of the LCD device to cause the LCD device to display data with a visible contrast ratio beyond the normal, manufacturer-specified operational temperature range, or to improve the contrast of displayed data at upper regions of the normal temperature range.
In a still further aspect of the invention, a liquid crystal display device temperature compensation control system is disclosed. This system controls contrast control parameters including a contrast voltage applied to an LCD device; a frame rate with which data is provided to the LCD device for display; and an inversion state of the displayed data. The contrast control parameters are adjusted such that the LCD device displays data with a particular contrast ratio.
In a still further aspect of the present invention, a defibrillator is disclosed. The defibrillator includes an LCD device that displays data with a contrast ratio that is dependent upon ambient temperature and a received contrast voltage. The LCD device displays data with a contrast ratio of less than one for a standard contrast voltage/ambient temperature operational range and an extended contrast voltage/ambient temperature operational range effective for ambient temperatures that are greater than or equal to temperatures defining the standard operational mode. The defibrillator also includes a device that controls the contrast voltage supplied to the LCD device such that it operates within either the standard or extended operating ranges based on ambient temperature to achieve an optimum contrast ratio.
In another aspect of the invention, a method for controlling the contrast voltage supplied to an LCD device is disclosed. The method includes the steps of (1) monitoring ambient temperature of the LCD device; and (2) supplying a contrast voltage to the LCD device. The contrast voltage is associated with a selected one of either a standard operating range of ambient temperatures or an extended operating range of ambient temperatures greater than the standard operating range of ambient temperatures. The contrast voltage is determined based on current ambient temperature and a selected operational mode.
Various embodiments of the present invention provide certain advantages and overcome certain drawbacks of the conventional LCD devices and traditional techniques for controlling the contrast with which data is displayed on such devices. Not all embodiments of the invention share the same advantages and those that do may not share them under all circumstances. This being said, the present invention provides numerous advantages including the noted advantage of controlling an LCD device so as to achieve an optimum contrast ratio for a given ambient temperature and, in particular, enabling the LCD device to display data with sufficient contrast at temperatures that are greater than standard operating temperatures. These and other features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.